1. Field of the Invention
The present invention relates to nonreciprocal circuit devices used in high-frequency bands such as a microwave band, for example, isolators, circulators, or the like.
2. Description of the Related Art
In general, a lumped-constant isolator has characteristics in which the amount of attenuation is extremely small in a signal-propagating direction as a forward direction and is extremely large in a reverse direction. This type of isolator is used, for example, in a transmission/reception circuit of a communication apparatus such as a mobile phone. In the recent mobile communication equipment, miniaturization and cost reduction of the equipment are being facilitated. Thus, in addition to that, there is a growing demand for reducing the sizes and costs of nonreciprocal circuit devices incorporated in the mobile communication equipment. In order to achieve the goal, a nonreciprocal circuit device using a quadrangular magnetic plate is provided.
Conventionally, when such a quadrangular magnetic plate is used, in order to keep the characteristic balance between ports, the magnetic plate has a rectangular shape. In addition, one of three central conductors is disposed in parallel to the long edges of the magnetic plate, and the remaining two central conductors are inclined to each edge of the magnetic plate so that the central conductors intersect each other at 120 degrees. For example, Japanese Unexamined Patent Application Publication No. 8-23212 discloses a nonreciprocal circuit device. In this nonreciprocal circuit device, the ratio of the long edge to the short edge of the magnetic plate is set to be 2 {square root over (3)} and one central conductor is disposed in parallel to the long edge and the lengths of central.conductors are equal.
Meanwhile, in the recent mobile communication equipment such as mobile phones, not only miniaturization but also reduction in power consumption has been strongly needed in order to achieve long-hour communications. Thus, the rectification of insertion losses, that is, the reductions in insertion losses in nonreciprocal circuit devices are being increasingly demanded. In addition, in nonreciprocal circuit devices incorporated in mobile phones, considering insertion losses between specified ports is thought to be important, while insertion losses between the remaining ports are of little concerns. Therefore, further reduction in the insertion losses between the specified ports is more required than maintaining of the characteristic balance between the ports.
However, when the sizes of the magnetic plates are reduced, usually, there is a tendency in which pass bandwidths become narrower and the insertion losses are deteriorated. As a result, in the nonreciprocal circuit devices having the above conventional structure, it is difficult to desirably reduce the insertion losses, although the characteristic balance between the ports can be maintained.
Accordingly, it is an object of the present invention to provide a compact and low-priced nonreciprocal circuit device capable of reducing an insertion loss, and a communication apparatus incorporating the same.
In order to accomplish the above object, according to an aspect of the present invention, there is provided a nonreciprocal circuit device including a magnetic member to which a DC magnetic field is applied, and three central conductors disposed on the magnetic member to intersect each other in an electrically insulated state. In this nonreciprocal circuit device, the magnetic member has a planar rectangular configuration having long and short edges, and one of the three central conductors is disposed in parallel to the short edges of the magnetic member.
With this arrangement, as described below, the insertion loss between the ports of the two central conductors apart from the central conductor disposed in parallel to the short edges of the magnetic member can be reduced. The reason for this is that the lengths of the two remaining central conductors become longer than the length of the central conductor disposed in parallel to the short edges of the magnetic member, thereby leading to the strengthening of a coupling between the two central conductors.
In addition, in this nonreciprocal circuit device, a terminating resistor may be connected to a port of the central conductor disposed in parallel to the short edges of the magnetic member so as to form an isolator.
In addition, the two central conductors apart from the central conductor disposed in parallel to the short edges of the magnetic member may intersect each other at an angle xcex8, which is greater than 120 degrees and less than 180 degrees. This arrangement permits the insertion loss to be reduced. This is because that the coupling between the two central conductors is strengthened by setting the intersecting angle xcex8 to be greater than 120 degrees.
In addition, in the nonreciprocal circuit device, each of the central conductors may be extended from a common grounding section to be bent on the magnetic member disposed on the grounding section, and the two central conductors apart from the central conductor disposed in parallel to the short edges of the magnetic member may intersect each other at an angle, which is greater than 120 degrees and less than or equal to 140 degrees. This is because, when the intersecting angle xcex8 is set to be greater than 140 degrees, the two central conductors apart from the central conductor parallel to the short edges of the magnetic member are mutually overlapped at the end portions of the magnetic member. As a result, the two conductors cannot be disposed by bending on the magnetic member.
According to another aspect of the present invention, there is provided a communication apparatus including the above nonreciprocal circuit device as an isolator. With this arrangement, power consumption of the communication apparatus can be reduced.